a) Field of the Invention
This invention relates to novel diols containing a perfluoroalkyl group or perfluoroalkenyl group, which will hereinafter be commonly abbreviated as an xe2x80x9cRf groupxe2x80x9d, and also to polyurethanes using the diols.
b) Description of the Related Art
Polyurethane is excellent not only in abrasion resistance, adhesion properties, flexibility, chemical resistance and the like but also in applicability to various molding or forming processes. Polyurethane are, therefore, widely used as binders in various coating materials, paints, inks and the like and also as raw materials for films, sheets and other molded or formed products. A wide range of polyurethanes suited for individual applications have been proposed. It is to be noted that the term xe2x80x9cpolyurethanexe2x80x9d as used herein collectively mean xe2x80x9cpolyurethanexe2x80x9d, xe2x80x9cpolyureaxe2x80x9d and xe2x80x9cpolyurethane-polyureaxe2x80x9d.
These polyurethanes are each obtained basically by reacting a polyol and/or a polyamine, a polyisocyanate and optionally, a chain extender, and depending on the kinds and combinations of these individual components, polyurethanes of various physical properties can be provided.
As one of such processes, it has been proposed to introduce an organic fluorine compound into a molecule of polyurethane by copolymerization so that the polyurethane is imparted with properties of the organic fluorine compound, such as water repellency and oil repellency, non-tackiness, abrasion resistance and anti-fouling property, while retaining its inherent good properties. For example, processes have been proposed for the production of fluorine-containing polyurethane, which make combined use of a one-end diol having an Rf group (the term xe2x80x9cone-end diolxe2x80x9d as used herein means xe2x80x9ca compound having two hydroxyl groups at only one end of its moleculexe2x80x9d) and a conventional diol other than the one-end diol (diols other than one-end diols will hereinafter be referred to simply as xe2x80x9cdiolsxe2x80x9d) (JP S43-26518 B, JP S61-252220 A).
As a conventional process for the preparation of a one-end diol having an Rf group, a process which, for example, proceeds following such a reaction scheme as will be described next is known. 
As is appreciated from the foregoing, the conventional processes for the preparation of one-end diols having the Rf group all require many steps. The one-end diols having the Rf group, which are obtained as high-purity products, are costly, so that these conventional processes have a problem in their practical use on an industrial scale.
In conventional polyurethanes each of which is available from combined use of a one-end diol having the Rf group and a diol, on the other hand, any attempt to make the polyurethanes exhibit functions of fluorine by increasing the contents of fluorine in the polyurethanes leads to reductions in certain inherent properties of the polyurethanes such as rubber elasticity and mechanical strength.
This is attributed to properties of the Rf groups that the resulting fluorine-containing polyurethane molecules are stiff and tend to orient in a particular direction because fluorine atoms are very bulky, produce strong repulsion therebetween and are closely packed in the molecules so that the molecular chains are hardly bendable. As a result, polyurethane is considered to be reduced in rubber elasticity due to a decrease in the thermal motion of soft segments in the molecular chains due to the Rf groups and/or to be reduced in strength due to inhibition to aggregation of hard segments.
The above-mentioned problem of polyurethanes in each of which a conventional one-end diol having an Rf group has been introduced is caused by strong effects of the Rf group on the polyurethane backbone as the Rf group and the polyurethane backbone are located close to each other.
An object of the present invention is, therefore, to provide an Rf-containing one-end diol, which can be prepared with high purity at low cost by simple steps, as a substitute for the conventional Rf-containing one-end diols each of which causes such a problem as mentioned above when employed as a diol component for polyurethane. Another object of the present invention is to provide a process for the preparation of the Rf-containing one-end diol. A further object of the present invention is to provide a novel Rf-containing polyurethane imparted with excellent water repellency and oil repellency, anti-fouling property, abrasion resistance, non-tackiness and the like without reductions in the inherent good properties of polyurethane.
The above-described objects can be achieved by the present invention as will be described hereinafter.
In one aspect of the present invention, there is thus provided a fluorine-containing diol represented by the following formula (I): 
wherein Rf represents a perfluoroalkyl or perfluoroalkenyl group having 1 to 20 carbon atoms; X represents a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenylene group represented by xe2x80x94CHxe2x95x90CHxe2x80x94(CH2)nxe2x80x94 in which n stands for an integer of from 1 to 10, or 
in which n stands for an integer of from 0 to 6; Y represents a direct bond, xe2x80x94Oxe2x80x94, xe2x80x94NHxe2x80x94, or xe2x80x94R0xe2x80x94NHxe2x80x94 in which R0 is an alkylene group having 1 to 6 carbon atoms; Z represents a direct bond or xe2x80x94N(Rxe2x80x2)Rxe2x80x94 in which R is an alkylene group having 1 to 20 carbon atoms and Rxe2x80x2 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; R1 and R2 each independently represent a divalent organic group; and R3 represents a residual group of an aliphatic, alicyclic or aromatic diisocyanate.
In another aspect of the present invention, there is also provided a process for the preparation of a fluorine-containing diol represented by the above-described formula (I), which comprises reacting a fluorine-containing compound, which has an Rf group and an active-hydrogen-containing group, with a diisocyanate at an NCO/OH ratio of approximately 2, and then reacting a resulting fluorine-containing group, which contains one free isocyanate group in a molecule, with a dialkanolamine at a temperature not higher than 50xc2x0 C.
In a further aspect of the present invention, there is also provided a fluorine-containing polyurethane obtained by reacting a fluorine-containing diol represented by the above-described formula (I), an aliphatic, aromatic or alicyclic diisocyanate, and an aliphatic, aromatic or alicyclic diol and/or a diamine, and optionally, a chain extender; the polyurethane having fluorine-containing side chains, which are represented by the following formula (II): 
wherein R1 to R3, Rf, X, Y and Z have the same meanings as defined claim 1
and which are bonded via R1 and R2 thereof to a backbone of the polyurethane by means of urethane bonds and/or urea bonds, at a content such that the polyurethane has a fluorine content of from 3 to 80 wt. %; and the polyurethane having a weight average molecular weight of from 5,000 to 500,000.
In a still further aspect of the present invention, there is also provided a fluorine-containing polyurethane as described above, which further comprises polysiloxane segments derived from a polysiloxane having at least one active-hydrogen-containing group.
In a still further aspect of the present invention, there is also provided a process for the production of a fluorine-containing polyurethane, which comprises reacting a fluorine-containing diol represented by the above-described fluorine-containing diol represented by the above-described formula (I), a diisocyanate, and a diol other than the fluorine-containing diol and/or a diamine, and optionally a chain extender.
In a still further aspect of the present invention, there is also provided a process for the production of a fluorine-containing polyurethane as described above, which comprises further reacting a polysiloxane having at least one active-hydrogen-containing group in an amount such that a content of polysiloxane segments in the polyurethane falls within a range of from 1 to 75 wt. %.
These novel polyurethanes obtained from the Rf-containing diol are excellent in surface propertiesxe2x80x94such as water repellency and oil repellency, anti-fouling property, abrasion resistance and non-tackinessxe2x80x94while retaining inherent good properties of polyurethane such as strength characteristics, rubber elasticity and low-temperature characteristics more sufficiently than polyurethanes making use of conventional Rf-containing diols.